X-ray crystallographic studies of tomato bushy stunt virus (TBSV), now successful at 2.9 Angstrom resolution, will be pursued in an effort to refine and extend the molecular-structural insights already obtained. In particular, we plan continued model-building and refinement at 2.9 Angstrom resolution, extension of data collection to 2.5 Angstrom and crystallographic studies of a recently-discovered expanded form of the virus. This work will enable us to define quite precisely the structural properties of a protein subunit with a flexible, multi-state hinge and to understand the role of an "unfolded" N-terminal arm that interdigitates during assembly with cognate aims of other subunits.